1. Field of Invention
The present invention relates to an apparatus and a method for purifying contaminated water by photochemical oxidation, wherein at least a sub-flow of water is directed through a flow channel wherein the water is irradiated with UV electromagnetic radiation from at least one UV lamp assembly.
2. Description of the Prior Art
An apparatus and a method of such kind are known from WO 99/33752. Polluted or contaminated water is discharged in large quantities, e.g. waste water from domestic residences and industries. The content of the waste water includes impurities that must be removed to a sufficient degree before the water is released to the recipient. This purification is carried out for instance in municipal cleaning installations where the contaminated water is subjected to a number of purification sub-processes for removing or eliminating the harmful effects of the impurities. The sub-processes include both biological and mechanical processes of treating the contaminated water with or without inactivating microorganisms with UV light.
The impurities may include environmentally harmful substances interfering biologically with the nature, including toxic substances and medical substances, and in particular hormone disruptive substances, such as e.g. dioxins, softeners, phthalates, and oestrogen from contraception pills. These hormonal interfering substances influence both humans, plants and animals and can cause serious genetic disorders. The known cleaning plants and methods do not particularly target these substances when purifying the contaminated water.
From U.S. Pat. No. 4,792,407, an oxidation process is known for reducing the environmentally harmful substances. According to this method, ozone is “bubbled” through the water and a UV low-pressure lamp radiating monochromic light with UV energy of 253 nm wave length is used. It is found that the use of monochromic UV radiation energy with the wave length of 253 nm and with the addition of ozone as bubbles, no creation of OH108  radicals and atomic oxygen O3P will occur, as otherwise expected. This known method however is very energy consuming and it has not been possible to achieve the desired results which were expected with respect to the creation of OH108  radicals and atomic oxygen O3P.
This is due to several factors. The UV low-pressure lamp with monochromic light has 100% intensity by 253.7 nm and the 8% interval is by 184.9 nm. Firstly, this type of lamps is normally intended for inactivating microorganisms and there is hardly any or no energy at all for photochemical fission reactions of the environmentally harmful substances where the required energy most of all is within the range of between 180 nm to 220 nm.
Secondly, the wave lengths required for the photo-oxidation with molecular oxygen must be lower than 200 nm. In order to obtain sufficient energy for the photo-oxidation in water contaminated with environmentally harmful substances, a large amount of UV low-pressure lamps with monochromic light energy must be applied. This is costly and thus not cost-effective for practical use in a large scale in a contaminated water treatment plant.
Thirdly, any possible photo-oxidation, which is generated at a wave length of 184.9 nm, is prevented by using the UV low-pressure lamp, due to reflection from the UV low-pressure lamp of the radiation having other wave lengths, e.g. of 253.7 nm, or by the adjacent lamps if a multiple of lamps are installed prevents the photo-oxidation.
In e.g. U.S. patent application No. 2002/0023866 A1 is described a method of bringing bubbles of ozone in water. From WO97/29997 is known a method of disperging micro bubbles in water.
When ozone is added as bubbles in water and is radiated with monochromic UV light having a wavelength of 253.7 nm, the bubbles absorb the UV energy and oxygen and heat is created without a photo-oxidation is achieved.
The known water purification plants which are used for the oxidation process use a large amount of ozone, hydrogen peroxide and/or other oxidation means relative to the obtained cleaning effect. The reaction time is very long and a large amount of UV lamps with monochromic light must be applied. This results in that this plant is expensive in both installation and operation and the environmentally harmful, hormone affecting, disruptive substances are only partially eliminated if any elimination takes place at all.